The invention relates to the correction of errors in a television picture, and particularly to an error correction circuit which performs horizontal and vertical interpolation to provide error correction waveforms in a camera head during the camera operating mode.
Various systems are available for measuring selected errors in a television picture and for selectively storing the measured errors, during a camera setup mode. During the subsequent camera operating mode, the error correction waveforms corresponding to the measured errors are applied via an error correcting system located in the camera head, to various control inputs, scan deflectors, etc, to correct the given errors in the picture. Such systems utilize accordingly, an error measurement circuit generally removed from the camera head and which must be coupled, generally via cables, to the camera head to retrieve the stored error data during the camera operating mode.
Predominant among such correction schemes are those employing analog sources such as potentiometers, integrators, capacitors, etc., wherein the measured errors are encoded, multiplexed and decoded, thereby requiring considerable analog circuitry which in some systems, may generate considerable drift and thus stability problems. The analog sources must be read and continually re-adjusted, whereby the camera head, i.e., the correction circuit, is usually continually dependent upon the signals from the measurement circuit.
Recent improvements in error measurement and correction systems have included a remotely-located analog measurement circuit, which automatically generates error measurement signals during the setup mode and supplies the signals in digital form to a digital error correction circuit located in the camera head. The measured error data are measured by a differential sample value technique and are digitally stored in the camera head for subsequent use by the error correction circuit therein independently of the error measurement circuit, during the camera operating mode. During the camera operating mode, the correction circuit digitally reads out the differential data, performs an interpolation from correction point to correction point and converts the differential data to absolute values, generates analog error voltage waveforms which are superimposed on the basic deflection waveforms to correct, for example, horizontal and vertical spatial errors. Shading error correction signals are retrieved, converted to analog signals, and are fed to the video processing circuit to correct any shading errors.
Such an error correction circuit has the disadvantage of being generally complex in circuitry and lacking in the degree of accuracy which is presently desirable in spatial error measurement and corrector circuits.
Typical of the above prior art analog error measurement and digital error correction system is the system described in co-pending application to E. F. Morrison et al, Ser. No. 124,370 filed Feb. 25, 1980, and assigned to the same assignee as this application.